In the very early days of semiconductor device fabrication, the individual devices were separated from the other devices fabricated on the wafer by using the dicing process of scribing and breaking. The scribing process was carried out using a sharp-tipped diamond tool and initially done by hand. Later, automatic scribing machines such as those described in U.S. Pat. Nos. 3,094,785 and 5,820,006 were developed. These scribing machines provided a way to precisely position the diamond scribe tip as it traversed the width of the wafer and created the scribe line. This is necessary because the scribe line must stay within the scribe street that can be as narrow as 50 microns in width. Problems were observed with these scribe machines when hard semiconductor materials such as silicon were scribed. The diamond tips used in the machines would wear down quickly and have to be changed frequently at some expense. A new technology developed to dice these hard semiconductor materials using very thin saw blades made up of diamond particles embedded in a metal or resin matrix. Most silicon devices are currently diced using this sawing technology. The fact that the saw blade requires a wider scribe street due the width of the blade was generally not considered a problem, as silicon material is not too costly to produce. At this time, scribing with a sharp-tipped diamond tool is used primarily in niche applications in which the material is relatively soft so as not to cause a problem with diamond scribe tool life and in which the material is relatively expensive to produce. The materials that fit these criteria are generally compound semiconductors like gallium arsenide and indium phosphide.
For many decades, scribing and breaking of glass has been done using a wheel fabricated of steel or tungsten carbide. This wheel has an angle formed along its periphery that is pressed into the glass as it rolls along to create the scribe line. In the assembly of the scribe tool, the scribing wheel is mounted on an axle through a hole in its center. Then the axle and scribing wheel are placed in a tool body with holes on both sides to support the axle. The scribe tool is typically placed in a glass scribing machine similar to the one described in U.S. Pat. No. 4,221,150. In a glass scribing tool there are at least 50 to 100 microns clearance between the sides of the scribe of the scribe wheel and the inside of the yoke to allow the scribe wheel to turn freely. Therefore, when the scribe wheel tool traverses the glass to form the scribe line, the scribe wheel can move laterally back and forth between the inside edges of the yoke. This causes the scribe line to vary from a straight line by 50 to 100 microns. In glass scribing this variation is not considered a problem because the size of the scribed glass does not need to be held to any tighter tolerances.
In certain new types of semiconductor devices made out of silicon materials, the use of saws to dice wafers has proven to be unsatisfactory. In MEMS devices, the debris created by the sawing processing can prevent the mechanisms from operating properly. In very thin integrated circuits, such as those used in smart cards, the protruding diamond particles in the blade can cause chipping and fracturing of the device die. In trying to develop a process to dice these devices, conventional scribing using a sharp-tipped diamond tool was tried. While this approach solved the problem with debris and reduced chipping and fracturing, short diamond tool life when scribing a hard material like silicon is still a problem.
The purpose of the invention of above-identified application Ser. No. 11/041,841 is to achieve longer tool life, while maintaining the advantages of scribing over sawing in certain applications. The invention encompasses a new scribing tool and a new method of scribing semiconductor wafers employing the tool.
The scribing tool of above-identified application Ser. No. 11/041,841 is for use in semiconductor scribing apparatus for dicing semiconductor wafers. The scribing tool includes a tool body for movement relative to a semiconductor wafer, the tool body having a yoke with yoke legs defining a space therebetween.
A semiconductor wafer scribing wheel is located in the space having opposed scribing wheel sides an outer peripheral angularly disposed, converging scribed surfaces extending outwardly from the sides engageable with the semiconductor wafer to form scribed lines therein when the tool moves relative to the semiconductor wafer and exerts pressure thereon. The semiconductor wafer scribing wheel defines a central opening extending between the opposed scribing wheel sides.
An axle passes through the central opening and projects from the opposed scribing wheel sides, the axle cooperable with the yoke legs to rotatably support the semiconductor wafer scribing wheel within the space whereby the semiconductor wafer scribing wheel rotates when in engagement with the semiconductor wafer and the tool moves relative thereto.
Bearings are engageable with the opposed scribing wheel sides to resist sideways deflection of the semiconductor wafer scribing wheel during rotational engagement thereof with the semiconductor wafer.
The method of above-identified application Ser. No. 11/041,841 includes the step of supporting a semiconductor wafer on a support.
A scribing tool is positioned above the supported semiconductor wafer, the scribing tool including a tool body having a yoke with yoke legs defining a space therebetween, a semiconductor wafer scribing wheel in the space and an axle having a longitudinal axis extending between the yoke legs and supporting the semiconductor wafer scribing wheel for rotation about a rotational axis coaxial with the longitudinal axis.
The method also includes the step of bringing the semiconductor wafer scribing wheel into engagement with the semiconductor wafer.
Pressure is exerted on the semiconductor wafer with the semiconductor wafer scribing wheel.
While maintaining the pressure on the semiconductor wafer with the semiconductor wafer scribing wheel, relative movement is caused between the scribing tool and the semiconductor wafer to move the semiconductor wafer scribing wheel across a surface of the semiconductor wafer while rotating the semiconductor wafer scribing wheel about the rotational axis to form a scribe line in the semiconductor wafer.
During any dicing process of semiconductor wafers or similar substrates, including the process disclosed in application Ser. No. 11/041,841, small particles of the substrate material are sometimes created by the dicing tool cutting into the material of the substrate. In some types of devices these particles can cause problems in the functioning of the devices fabricated on the substrate. For example, MEMS devices may have intricate mechanisms fabricated on the surface of the substrate. Particles of material from the substrate can get into the mechanisms and prevent them from operating properly. Once particles are deposited on the surface of the substrate they may be held in place by static electricity and can be very difficult to remove without damaging the devices.